Energetic nitro malonate polyester binders

ABSTRACT

Liquid nitromalonate polyesters and methods for their preparation are disclosed. Solid propellants are provided which employ as the binder a nitromalonate polyester. These propellants are resistant to plasticizer syneresis and crystallization and provide an increase in the specific impulse of the propellant.

The U.S. Government has a nonexclusive, nontransferable, royalty-freelicense to make, use, or sell the invention pursuant to Contract Nos.DAAH01-83-C-A076 and DAAH01-85-C-0587 awarded by The Department of theArmy to Morton Thiokol, Inc.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to novel nitromalonate polyesters, to methods forpreparing said nitromalonate polyesters, and to solid propellants whichcomprise a binder, an oxidizer, a plasticizer and, optionally, ametallic fuel wherein the binder is a nitromalonate polyester.

2. Description of the Prior Art

Solid propellants are commonly made by preparing a mixture of a finelydivided organic or inorganic oxidizing agent, a metallic fuel, a liquidpolymer binder, a curing agent for the polymer, a plasticizer and minoramounts of various modifying ingredients, introducing the resultingmixture into a motor casing and curing the mixture. The cured polymeracts both as a fuel for reaction with the oxidizing agent and as abinder to provide the propellant with the desired physical properties.

One problem with solid propellants has been that, when a plasticizer wasemployed in the propellant composition, the propellant frequently wassubject to plasticizer syneresis and crystallization. Attempts were madeto overcome this problem and at least partial success was met withpropellants which employed a combination of polyethylene glycol (PEG)and polycaprolactone (PCP) as the binder and a plasticizer which was amixture of trimethylolethane trinitrate (TMETN) and butanetrioltrinitrate (BTTN). This combination of PEG/PCP binder and TMETN/BTTNplasticizer was found to produce minimum smoke propellants which hadexcellent strain capability under low temperature storage and cyclingconditions. These propellants were also less prone to crystallization ofeither the polymer binder or plasticizer. They were further found to beresistant to plasticizer exudation or synersis at intermediate lowtemperatures such as 0° to -20° F. The combination of plasticizers wasfound to be a very important factor in the prevention of crystallizationat low temperatures. In fact, certain plasticizers or combinations ofplasticizers, such as TMETN and 1/1 mixtures of TMETN and BTTN;crystallize after low temperature storage and cause severe loss inpropellant strain capability to a level of less than 1-2%.

While the combination of 1 part TMETN and 2 parts BTTN does provideacceptable propellant properties, due to the very high cost of BTTN itwould be highly desirable to develop a propellant which eliminates ordecreases the level of BTTN needed to prevent plasticizercrystallization while still maintaining the desirable physicalproperties and burn characteristics of the propellant.

Demands for higher performance, longer range minimum smoke rocketmissions are a recurring theme by all military services as secondgeneration rocket motor requirements approach or exceed the limitsimposed by present state-of-the-art materials. Though these demandsexist for strategic and strap-on launch applications, the most stringentrequirements are mandated by tactical application. The tacticalenvironment imposes high and low temperature requirements on thepropellants which can severely limit the utilization of otherwiseattractive propellant ingredients. Problems encountered includelimitations of shelflife imposed by marginal high-temperature stabilityand propellant cracking and/or plasticizer syneresis. All of theseproblems have in tensified as higher levels of nitrate esterplasticizers have been used to approach the performance requirements ofcurrent systems. The inherent thermal instability of nitrate esters,volatility, tendency toward phase separation and crystallization at lowtemperature impose important trade-off considerations which can limittheir utilization. On the other hand, propellant processing andmechanical property requirements also place upper limits on the level ofnitramines which can be formulated.

State-of-the-art polymer ingredients, with the exception ofnitrocellulose, are non-energetic materials. Because minimum smokepropellants, in general, are under-oxidized since the nitramine"oxidizers" are actually monopropellants, the inert polymer causes asteep decline in specific impulse as the plasticizer/polymer ratio isdecreased. If sufficiently stable energetic or oxidizing groups can beincorporated into the polymer without otherwise degrading the binderproperties, then the propellant performance and specific impulse can besignificantly increased.

Another important consideration in designing high energy polymers is thecomposition of the exhaust gases after combustion. Higher oxygen contentbinders reduce the content of hydrogen and carbon monoxide in theexhaust gases. Reducing these fuel-rich gases is necessary if theafterburning of the exhaust plume is to be effectively minimized. Thisconsideration, along with smoke reduction, is important in designingminimum signature rocket motors.

Historically, the original high-energy polymeric material wasnitrocellulose. Although nitrocellulose was used early for non-energeticapplications such as motion picture film and billiard balls, itsprinciple use has been in the explosives and munitions industry.Depending on the degree of nitration of the cellulose, the cellulose andthe materials with it is mixed, nitrocellulose finds applications insmokeless powder and double-base propellants. The nitrate ester linkage(RONO₂) present in nitrocellulose provides a very high and energeticoxygen content; however, like the nitrate ester plasticizers such asnitroglycerine, nitrocellulose has marginal thermal stability fortactical environmental scenarios.

In recent years, other energetic functional groups have beenincorporated into polymers as well as plasticizer and oxidizermaterials. In some cases, such as the extensive research and developmenteffort into organic nitrogen-fluorine chemistry in the 1960's, nomaterials are currently being considered for high energy applications.Factors which have limited the application of N-F compounds includecost, chemical stability, and sensitivity.

It will be noted that nearly all of the high-energy polymers currentlyunder investigation are hydroxyl functional. These materials, inconjunction with an isocyanate cure agent, are favored in minimum smokeformulations which contain nitrate esters because of excellentcompatibility. Other potential functional groups such as carboxylic acidand thiols, which have been used in composite propellant formulations,are incompatible with nitrate esters. This requirement and the readyavailability of a wide variety of hydroxyl-terminated polymers has ledto their favored position for use in minimum smoke binders.

Thus, it would be highly desirable to provide a polymeric binder forsolid propellants which is compatible with the other propellantingredients, provides acceptable propellant physical properties,prevents or minimizes plasticizer syneresis and crystallization and hasa high-energy potential which will contribute to the propellant'sspecific impulse.

SUMMARY OF THE INVENTION

In accordance with the present invention there are provided liquidpolymers comprising nitromalonate polyester. These nitromalonatepolyesters include polymers of the general formula: ##STR1## where R¹and R² are the same or different and are selected from --NO₂, --R³ ONO₂,alkyl, --F and --H with the proviso that at least one of R¹ and R² is--NO₂ or --R³ ONO₂ ;

R³ is alkylene;

X is ##STR2## R⁵ is --CH═CH-- or --CH₂ CH₂ --; R⁶ is alkylene;

n is at each independent occurrence an integer from 1 to about 40; and

x is an integer, preferably from 1 to about 40.

Also in accordance with this invention there are provided improved solidpropellants comprising a polymeric binder, binder curing agent,oxidizer, optional metallic fuel, and a plasticizer, wherein theimprovement comprises employing as the binder an effective amount of apolymeric binder which is a nitromalonate polyester. These nitromalonatepolyesters include those defined by formula (I) above. This inventionfurther provides such improved solid propellants which contain aplasticizer that is substantially free of butanetriol trinitrate.

There is further provided in accordance with this invention a method ofpreparing a nitromalonate polyester comprising:

A. reacting malonic acid or a derivative thereof and a slight excess ofa diol to form a hydroxy-terminated malonate polyester of the formula:##STR3## wherein R⁴ is alkyl; n is at each independent occurrence aninteger from 1 to about 40; and

x is are integer, preferably from 1 to about 40;

a is 0 or 1, b is 1 or 2 and a+b=2;

B. end-capping the hydroxy-terminated malonate polyester formed in stepA with a cyclic anhydride to form a malonate polyester of the formula:##STR4## wherein R⁴, n, x, a and b are as previously defined; and R⁵ is--CH═CH-- or --CH₂ CH₂ --; and

C. nitrating the product of step B with HNO₃ to produce a nitromalonatepolyester of the formula: ##STR5## wherein R⁴, n, x, a, b and R⁵ are aspreviously defined.

In accordance with the present invention there is also provided a methodfor preparing a nitromalonate polyester comprising:

A. reacting malonic acid or a derivative thereof and a slight excess ofa diol to form a hydroxy-terminated malonate polyester having theformula: ##STR6## wherein R⁴ is alkyl; n is at each independentoccurrence an integer from 1 to about 40;

x is and integer, preferably from 1 to about 40;

a is 0 or 1, b is 1 or 2 and a+b=2;

B. end-capping the hydroxy-terminated malonate polyester formed in stepA with a cyclic anhydride to form a malonate polyester of the formula:##STR7## wherein R⁴, n, x, a and b are as previously defined; and R⁵ is--CH═CH-- or --CH₂ CH₂ --;

C. reacting the product formed in step B with formaldehyde to form ahydroxymethylated malonate polyester of the formula: ##STR8## whereinR⁴, n, x, a, b and R⁵ are as previously defined; D. nitrating theproduct of step C with HNO₃ to produce a nitromalonate polyester of theformula: ##STR9## wherein R⁴, n, x, a, b and R⁵ are as previouslydefined.

The present invention also provides a method for preparing anitromalonate polyester comprising:

A. reacting malonic acid or a derivative thereof and a slight excess ofa diol to form a hydroxy-terminated malonate polyester of the formula:##STR10## wherein R⁴ is alkyl; n is at each independent occurrence aninteger from 1 to about 40; and

x is are integer, preferably 1 to about 40;

B. end-capping the hydroxy-terminated malonate polyester formed in stepA with a cyclic anhydride to form a malonate polyester of the formula:##STR11## wherein R⁴, n, and x are as previously defined; and R⁵ is--CH═CH-- or --CH₂ CH₂ --; and

C. nitrating the product of step B by reacting it with HNO₃ to produce anitromalonate polyester of the formula: ##STR12## wherein R⁴, n, x, andR⁵ are as previously defined; D. reacting the product of step C withformaldehyde to form a hydroxymethylated malonate polyester of theformula: ##STR13## wherein n, x and R⁵ are as previously defined; and E.nitrating the product formed in step D by reacting it with HNO₃ to forma nitromalonate polyester of the formula: ##STR14## wherein n, x and R⁵are as previously defined.

This invention also provides a method for preparing a nitromalonatepolyester comprising:

A. reacting malonic acid or a derivative thereof and a slight excess ofa diol to form a hydroxy-terminated malonate polyester of the formula:##STR15## wherein R⁴ is alkyl; n is at each independent occurrence aninteger from 1 to about 40; and

x is are integer, preferably from 1 to about 40;

B. end-capping the hydroxy-terminated malonate polyester formed in stepA with a cyclic anhydride to form a malonate polyester of the formula:##STR16## wherein R⁴, n, and x are as previously defined; and R⁵ is--CH═CH-- or --CH₂ CH₂ --;

C. nitrating the product of step B with HNO₃ to produce a nitromalonatepolyester of the formula: ##STR17## wherein R⁴, n, x and R⁵ are aspreviously defined; and D. reacting the product of step C with fluorineto produce a fluorinated nitromalonate polyester of the formula:##STR18##

This invention further provides a method for preparing ahydroxy-terminated polyester comprising:

A. reacting malonic acid or a derivative thereof and a slight excess ofa diol to form a hydroxy-terminated malonate polyester of the formula:##STR19## wherein R⁴ is alkyl; n is at each independent occurrence aninteger from 1 to about 40; and

x is are integer, preferably from 1 to about 40;

a is 0 or 1, b is 1 or 2 and a+b=2;

B. end-capping the hydroxy-terminated malonate polyester formed in stepA with a cyclic anhydride to form a malonate polyester of the formula:##STR20## wherein R⁴, n, x, a and b are as previously defined; and R⁵ is--CH═CH-- or --CH₂ CH₂ --;

C. nitrating the product of step B with HNO₃ to produce a nitromalonatepolyester of the formula: ##STR21## wherein R⁴, n, x, a, b and R⁵ are aspreviously defined; and D. reacting the nitromalonate polyester formedin step C with an alkylene oxide or a polyol (as by reacting the productof step C with SOC1₂ followed by reaction with the polyol) to form ahydroxy-terminated nitromalonate polyester of the formula: ##STR22##where R⁶ is alkylene or hydroxy-substituted alkylene.

A method of preparing a hydroxy-terminated nitromalonate polyester isalso provided by the present invention comprising:

A. reacting malonic acid or a derivative thereof and a slight excess ofa diol to form a hydroxy-terminated malonate polyester having theformula: ##STR23## wherein R⁴ is alkyl; n is an integer from 1 to about40;

x is and integer, preferably from 1 about 40; and

a is 0 or 1, b is 1 or 2 and a+b=2;

B. end-capping the hydroxy-terminated malonate polyester formed in stepA with a cyclic anhydride to form a malonate polyester of the formula:##STR24## wherein R⁴, n, x, a and b are as previously defined; and R⁵ is--CH═CH-- or --CH₂ CH₂ --;

C. reacting the product formed in step B with formaldehyde to form ahydroxymethylated malonate polyester of the formula: ##STR25## whereinR⁴, n, x, a, b and R⁵ are as previously defined; D. nitrating theproduct of step C with HNO₃ to produce a nitromalonate polyester of theformula: ##STR26## wherein R⁴, n, x, a, b and R⁵ are as previouslydefined; and E. reacting the product formed by step D and an alkyleneoxide or a polyol (as by reacting the product of step D with SOC1₂followed by reaction with polyol) to form an hydroxy-terminatednitromalonate polyester of the formula: ##STR27## where R⁶ is alkyleneor hydroxy substituted alkylene.

In accordance with the present invention there is further provided amethod for preparing an hydroxy-terminated nitromalonate polyestercomprising:

A. reacting malonic acid or a derivative thereof and a slight excess ofa diol to form a hydroxy-terminated malonate polyester of the formula:##STR28## wherein R⁴ is alkyl; n is at each independent occurence aninteger from 1 to about 40; and

x is are integer, preferably from 1 to about 40;

B. end-capping the hydroxy-terminated malonate polyester formed in stepA with a cyclic anhydride to form a malonate polyester of the formula:##STR29## wherein R⁴, n and x are as previously defined; and R⁵ is--CH═CH-- or --CH₂ CH₂ --;

C. nitrating the product of step B with HNO₃ to produce a nitromalonatepolyester of the formula: ##STR30## wherein R⁴, n, x and R⁵ are aspreviously defined. D. reacting the product of step C and formaldehydeto form a hydroxymethylated malonate polyester of the formula: ##STR31##wherein n, x and R⁵ are as previously defined; E. nitrating the productformed in step D by reacting it with HNO₃ to form a nitromalonatepolyester of the formula: ##STR32## wherein n, x and R⁵ are aspreviously defined; and F. reacting the product formed by step E and analkylene oxide or a polyol (as by reacting the product of step E withSOC1₂ followed by reaction with the polyol) to form anhydroxy-terminated nitromalonate polyester of the formula: ##STR33##wherein n, x and R⁵ are as previously defined and R⁶ is alkylene orhydroxy substituted alkylene.

This invention also provides a method for preparing a hydroxy-terminatednitromalonate polyester comprising:

A. reacting malonic acid or a derivative thereof and a slight excess ofa diol to form a hydroxy-terminated malonate polyester of the formula:##STR34## wherein R⁴ is alkyl; n is at each independent occurrence aninteger from 1 to about 40; and

x is an integer, preferably from 1 to about 40;

a is 0 or 1, b is 1 or 2 and a+b=2;

B. end-capping the hydroxy-terminated malonate polyester formed in stepA with a cyclic anhydride to form a malonate polyester of the formula:##STR35## wherein R⁴, n and x are as previously defined; and R⁵ is--CH═CH-- or --CH₂ CH₂ --;

C. nitrating the product of step B with HNO3 to produce a nitromalonatepolyester of the formula: ##STR36## wherein R⁴, n, x and R⁵ are aspreviously defined; D. reacting the product of step C with fluorine toproduce a fluorinated nitromalonate polyester of the formula: ##STR37##wherein n, x and R⁵ are as previously defined; and E. reacting theproduct formed by step D and an alkylene oxide or polyol (as by reactingthe product of step D with SOC1₂ followed by reaction with the polyol)to form an hydroxy-terminated nitromalonate polyester of the formula:##STR38## where n, x and R⁵ are as previously defined and R⁶ is alkyleneor hydroxy substituted alkylene.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical presentation of the amount ofN-methyl-4-nitroaniline (MNA) in poly (triethylene glycol nitro methylmalonate) vs. time (see Example 2).

FIG. 2 is a graphical presentation of the HAAKE viscosity of thepropellant of Example 2 vs. time.

FIG. 3 is a graphical presentation of the burn rate of the propellant ofExample 3 vs. pressure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The polymers of this invention are nitromalonate polyesters. As usedherein, the term "nitromalonate polyesters" refers to polymers made frommalonic acid (or a derivative thereof) and a diol which is subsequentlynitrated to introduce NO₂ or ONO₂ groups onto the polymer backbone.Thus, the nitromalonate polyesters of this invention include polymershaving the following general formula: ##STR39## where R¹ and R² are thesame or different and are selected from --NO₂, --R³ ONO₂, alkyl, --F and--H with the proviso that at least one of R¹ and R² is --NO or --R ONO₂;

R³ is alkylene; ##STR40## R⁵ is --CH═CH-- or --CH₂ CH₂ --; R⁶ isalkylene;

n is at each independent occurrence an integer from 1 to about 40; and

x is an integer, preferably from 1 to about 40.

As used herein, the term "alkyl" refers to monovalent, straight orbranched chain C₁ to C₄ hydrocarbyl groups, e.g. methyl, ethyl, butyland the like. The term "alkylene" refers to divalent, straight orbranched chain hydrocarbyl groups, e.g. ethylene.

The preferred nitromalonate polyesters of this invention are thoseaccording to formula (I) above where both R¹ and R² are --CH₂ ONO₂. Whenused as a propellant binder, these nitromalonate polyesters provide asignificant increase in the specific impulse (I_(sp)) of a propellantwhen compared to non-nitrated binders such as polycaprolactone (PCP) orpolyethylene glycol (PEG).

The nitromalonate polyesters of this invention may be prepared by any ofseveral processes depending upon the functional groups which are desiredto be introduced onto the polymer backbone or as terminal groups or thepolymer. These processes all begin with the preparation of a malonatepolyester, such as those according to formula (I). The preparation ofthese malonate polyesters is described in Korshak, et al., Doklady Akad.Nauk S. S. S. R. 94, 61-4 (1954) (Chem. Abst. 49:3823h (1955)) which ishereby incorporated by reference.

The processes of this invention are described in detail below. For thesake of brevity and clarity, the intermediates and products formed inthese processes are referred to simply by formula numbers whichcorrespond to the number formulas in the Summary of the Invention.##STR41##

Not all of the exact reaction conditions and procedures (temperatures,reaction times, product recovery procedures and the like) are indicatedin the foregoing processes of the present invention, but it is believedthat given the above disclosure, one of ordinary skill in the art candetermine these reaction conditions and procedures without undueexperimentation. In the above processes, the preferred cyclic anhydridesare succinic and maleic anhydride, most preferably maleic anhydride.

The quantities of the reactants used in the foregoing processes may alsovary depending upon the product desired. For example, in the nitrationsteps, if full nitration of the polymer is desired an excess of HNO₃(e.g. 3-5 times the stoichrometric amount) should be employed. If alower degree of nitration is desired, lesser amounts of HNO₃ should beemployed. Likewise, when the malonic acid or derivative and the diol arereacted to form the polymer a slight excess of diol (i.e. the molarratio of diol to malonic acid or derivative is slightly higher than 1:1)should be used. In general, the other reactions shown above shouldemploy a slight excess of reactant to ensure complete reaction. As withthe aforementioned reaction conditions, it is believed that, given theabove disclosure, one of ordinary skill in the art can determine theproper amounts of reactants needed to produce the desired productwithout undue experimentation.

The nitromalonate polyesters of this invention are useful as binders forsolid propellants. They are especially attractive as high-energy bindersfor minimum smoke propellants for the following reasons:

1. The nitromalonate polyesters have a high oxygen content which yieldsan increase in I_(sp) even at relatively low levels of nitration.

2. The nitromalonate polyesters have relatively fluid properties forsuch highly oxygenated materials, which means lower melting points andglass transition temperatures for the polymer.

3. Being polyester, these polymers have better solubility andcompatibility with the nitrate esters commonly employed in propellantsthan most nitro-containing polymers, which are often high meltingsolids.

4. The nitromalonate polyesters possess the excellent thermal stabilityassociated with C--NO₂ type compounds.

5. These polymers possess good safety and compatibility characteristics.

6. They can be manufactured by simple processes from readily available,low cost starting materials.

7. Resistance of the propellant containing nitromalonate polyesters toplasticizer syneresis and crystallization is improved.

8. Use of the nitromalonate polyesters permits the use of plasticizersin the propellant which would ordinarily crystallize at low temperaturesin commonly used binders, and the plasticizer may be substantially freeof the expensive compound BTTN.

The solid propellants of this invention also contain a curing agent forthe polymer binder. The curing agent must be capable of reacting withthe terminal groups on the polymer. When the terminal groups arehydroxyl groups the curing agents can include dicarboxylic compoundsalthough di- or polyisocyanates are preferred. Examples of suitableisocyanates include arylene polyisocyanates such as tolylenediisocyanates; meta-phenylene diisocyanate; 4-chloro-1, 3-phenylenediisocyanate; methylene-bis-(4-phenyl isocyanate); 1, 5-naphthalenediisocyanate; 3, 3'-dimethoxy -4, 4'biphenylene diisocyanate; 3,3+-diphenyl-4, 4'-biphenylene diisocyanate; triphenylmethanetriisocyanate; and alkylene poly-isocyanates such as methylene;ethylene; propylene-1, 2-; butylene-1, 3-; hexylene-1, 6- andcyclohexylene-1, 2-diisocyanates. Mixtures of poly-isocyanates may alsobe used. Desmodur N-100 isocyanate curing agent is most often used. Whenthe terminal groups on the nitromalonate polyester are carboxyl groups,the useful curing agents include polyfunctional epoxides andacylaziridines.

Any oxidizer commonly employed in solid propellants may be used in thepropellants of this invention. These exemplary oxidizers includeammonium perchlorate, lithium perchlorate, potassium perchlorate, sodiumperchlorate, ammonium chlorate, potassium chlorate, sodium chlorate,ammonium nitrate, lithium nitrate, sodium nitrate, ammonium picrate andthe like, and nitramines such as RDX and HMX.

The propellants of this invention also contain a plasticizer, preferablya so-called "energetic plasticizer" which not only effects propellantsphysical properties, but also contributes to the propellant burn rateand overall energy content. The plasticizer is employed to reducepropellant viscosity, increase propellant strain capacity at lowtemperature, increase propellant casting life, increase propellant burnrate and energy content and increase pot life. In order for theplasticizer to perform these functions it is essential that theplasticizer not be subject to syneresis or crystallization, even at lowtemperature.

Because they are energetic plasticizers the nitrate esters are preferredin the practice of this invention. These nitrate esters include, but arenot limited to, nitroglycerin; mono-, di- and triethyleneglycoldinitrate; nitrosobutylglycerol trinitrate; trimethylolethanetrinitrate; trimethylolmethane trinitrate. Butanetriol trinitrate mayalso be used as a plasticizer, but it is very expensive. Indeed, one ofthe advantages of this invention is that when the polymer binders of theinvention are employed, butanetriol trinitrate need not be used as aplasticizer whereas its use is essential with other binders.

The metallic fuel, when used in the propellants of this invention, iscommonly a powdered metal, preferably aluminum powder.

Other additives may, of course, be employed in the propellant includingburn rate enhancers, bonding agents, cure catalysts and the like.

The components of the propellants of this invention may be employed inthe amounts indicated in Table A below.

                  TABLE A                                                         ______________________________________                                        Amount (wt % based on total propellant weight)                                                  GENERAL   PREFERRED                                         COMPONENT         RANGE     RANGE                                             ______________________________________                                        Nitromalonate polyester binder                                                                   3-20      5-10                                             Curing agent      0.2-5.0   0.5-2.0                                           Oxidizer          30-80     50-70                                             Plasticizer        5-40     10-30                                             Fuel               0-30      0-20                                             ______________________________________                                    

The solid propellants of this invention may be prepared by conventionaltechniques. For example, the binder components may be mixed together(except that the curing agent may be withheld until after all othercomponents are mixed) and then the metallic fuel, if used, may be mixedwith the binder followed by addition of the oxidizer. The propellant maythen be cured in a conventional manner.

EXAMPLE 1

Nitromalonate polyesters were prepared as described in the table below.

    ______________________________________                                                     Product   Temperature/                                           Reaction Mixture                                                                           Yield     Time        Remarks                                    ______________________________________                                        5.0 g CM-TEGM.sup.1                                                                        5.6 g/93% Added HNO.sub.3                                                                           Extracted                                  50 ml CH.sub.2 Cl.sub.2 solvent                                                                      over 0.5 hr.                                                                              product                                    37.5 ml fuming         Started at  from ice                                   HNO.sub.3 (90%)        10° C. warmed                                                                      quench with                                                       slowly to   CH.sub.2 Cl.sub.2                                                 30° C. Total                                                                       H.sub.2 O wash,                                                   time, 4.5 hr.                                                                             dried over                                                                    Na.sub.2 SO.sub.4.                                                            Nitration                                                                     was incom-                                                                    plete. No                                                                     polymer de-                                                                   gradation.                                 5.0 g TEGM.sup.2                                                                           5.3 g/88% Added HNO.sub.3                                                                           Same work-                                 50 ml CH.sub.2 Cl.sub.2 solvent                                                                      over 0.67 hr.                                                                             up as                                      37.5 ml red fuming     Started at  above.                                     HNO.sub.3              10° C. warmed                                                                      Nitration                                                         slowly to   complete                                                          30° C. Total                                                                       (by NMR).                                                         time 4.5 hr.                                                                              No polymer                                                                    degra-                                                                        dation.                                    5.0 g DEGM.sup.3                                                                           5.6 g/89% Added HNO.sub.3                                                                           Same work-                                 50 ml CH.sub.2 Cl.sub.2 solvent                                                                      over 1.0 hr.                                                                              up as                                      50 ml fuming HNO.sub.3 Started at  above.                                     (90%)                  10° C. warmed                                                                      Nitration                                                         slowly to   90% com-                                                          30° C. Total                                                                       plete (by                                                         time, 5 hr. NMR). No                                                                      polymer                                                                       degra-                                                                        tion.                                      5.0 g EGM.sup.4                                                                            3.19 g wax                                                                              Added HNO.sub.3                                                                           Same work-                                 60 ml CH.sub.2 Cl.sub.2 solvent                                                            1.00 g solid                                                                            over 1.0 hr.                                                                              up as                                      100 ml fuming HNO.sub.3                                                                    mp.       Started at  above. Waxy                                (90%)        83-85° C.                                                                        10° C. warmed                                                                      portion                                                           to 30° C.                                                                          soluble in                                                        Total time, CH.sub.2 Cl.sub.2,                                                3 hr.       solid not.                                                                    Solid is                                                                      soluble in                                                                    acetone and                                                                   DMSO.                                      ______________________________________                                         .sup.1 Carbomethoxyterminated triethyleneglycol malonate polyester            .sup.2 Hydroxyterminated triethyleneglycol malonate polyester                 .sup.3 Hydroxyterminated diethyleneglycol malonate polyester                  .sup.4 Hydroxyterminated ethyleneglycol malonate polyester               

EXAMPLE 2

The thermal stability of poly (triethylene glycol nitro methyl malonate)(TEGNMM) was investigated. The rate of conversion ofN-methyl-4-nitroaniline (MNA) to N-nitroso-N-methyl-4-nitroaniline(NMNA) was used to determine the decomposition rate.

Two samples were prepared by dissolving 3.0 g of TEGNMM in 7.0 g oftriacetin. 1% MNA (w/w) was then added to both samples. 1.5% (w/w) ofPb₃ O₄ was then added to only one of the samples. As a comparison, asample of BTTN was prepared containing 1% (w/w) MNA. All three sampleswere placed in a 65° C. oven and removed on a weekly basis for analysis.

The results from aging the samples in the 65° C. oven for 105 days arepresented graphically in FIG. 1. As can be seen, TEGNMM is compatibleand stable at 65° C. for long periods of time.

EXAMPLE 3

The following minimum smoke propellant was prepared in a conventionalmanner using TEGNMM as the binder:

Propellant Composition

65.7% Total solids

22.84% Nitrate plasticizer

6.14% Polymer curing agent (Desmodur N-100 polyisocyanate) and additives

1/3.72 Polymer/plasticizer ratio

NCO/OH ratio=2/1

The propellant was subjected to standard safety testing in the uncuredstate. The results were as follows:

Impact 150 kg-cm

Spark 6.25 Joules

Friction 90 lbs.

Each number represents the point where the propellant failed to igniteor detonate.

The end-of-mix viscosity for the propellant was determined at 128° F.for a 500 g mix and 123° F. for the 400 g mix. The viscosities weredetermined using a Brookfield viscometer equipped with an "E" spindlewith a velocity of one rpm. The viscosities were 3.2 kp for the 400 gmix and 4.8 kp for the 500 g mix.

A potlife profile was determined using a HAAKE viscometer with a smoothcylinder and a shear rate of 0.294 sec⁻¹. The profile was determined at110° F. FIG. 2 is a potlife profile of a 500 g propellant mix preparedwith TEGNMM.

The burn rate of a 2-inch strand of the propellant was measured as afunction of pressure. The results are shown graphically in FIG. 3. Theburn rate at 1000 psi was 0.392 in/sec as compared to the baselineformulation (i.e., the propellant composition described above where a50/50 mixture of PEG and PCP is used as the binder instead of thenitromalonate polyester) which had a burn rate of 0.360 in/sec. Thisrepresents a 10% increase in burn rate.

The mechanical properties of the propellant were determined usinghalf-scale JANNAF tensile specimens at 77° C. The results are shown inTable B below.

                                      TABLE B                                     __________________________________________________________________________    (Half-Scale JANNAF Specimens, Crosshead Speed = 1 in/min)                               Secant                                                                              Strain                                                                            Nominal                                                                             Strain at                                                                           Max.     Strain Energy                        Specimen                                                                           Tangent                                                                            Modulus at                                                                          at Max.                                                                           Stress at                                                                           Max. Corr.                                                                          Corr.                                                                             Ultimate                                                                           Density to Max.                      No.  Modulus                                                                            10% Strain                                                                          Load                                                                              Max. Load                                                                           Stress                                                                              Stress                                                                            Strain                                                                             Corr. Stress                         __________________________________________________________________________    1    41.7 45.6  4.511                                                                             16.1  1.511 40.4                                                                              1.511                                                                              30.94                                2    45.7 47.8  1.296                                                                             14.3  1.296 32.9                                                                              1.315                                                                              22.84                                3    45.8 45.2  1.537                                                                             16.0  1.537 40.6                                                                              1.545                                                                              31.58                                4    42.2 43.1  1.391                                                                             15.0  1.391 35.8                                                                              1.398                                                                              26.15                                Avg. 43.9 45.4  1.434                                                                             15.4  1.434 37.4                                                                              1.442                                                                              27.88                                Std. Dev.                                                                          2.2  1.9   0.112                                                                             0.8   0.112 3.7 0.106                                                                              4.14                                 C.V. 0.0497                                                                             0.0421                                                                              0.0779                                                                            0.0550                                                                              0.0779                                                                              0.0998                                                                            0.0732                                                                             0.1485                               __________________________________________________________________________

The results shown in Table B indicate that the propellant had acceptablemechanical properties.

The thermal stability of the propellant made from the 400 g mix wasfollowed by MNA depletion at 165° C. The rate of MNA depletion wasdetermined by extracting a known amount of propellant with chloroformfollowed by GC analysis. Table C shows the relative amounts of MNA andN-nitroso MNA (NMNA) product for the propellant made in accordance withthe present invention and a similar propellant made from a mix of astandard formulation.

                  TABLE C                                                         ______________________________________                                        Nitromalonate Polyester                                                       Propellant           Comparison                                               TIME (Days)                                                                            MNA (%)  NMNA (%)   MNA (%)                                                                              NMNA (%)                                  ______________________________________                                         0       0.370    0.053      0.379  0.082                                      7       0.308    0.115      0.184  0.313                                     14       0.263    0.174      0.113  0.385                                     21       0.239    0.208      0.020  0.468                                     28       0.197    0.246                                                       35       0.175    0.290                                                       42       0.072    0.395                                                       ______________________________________                                    

EXAMPLE 4

Table D contains thermochemical calculations for conventional propellantbinder systems and for those in accordance with the present invention.It can be readily seen that the I_(sp) values for the nitromalonatepolyester binder systems of this invention are significantly higher thanthose of the conventional binders.

                  TABLE D                                                         ______________________________________                                                           H.sub.f   I.sub.sp (Lb Sec/Lb)                             Binder polymer                                                                           %0      (kcal/mole)                                                                             80% HMX/20% Polymer                              ______________________________________                                        Polycaprolactone                                                                         28.1    -103.2    216.4                                            Polyethylene glycol                                                                      36.4     -46.6    224.9                                            NEGM.sup.1 54.9    -179.6    245.2                                            DNDMEM.sup.2                                                                              61.53  -168.3    256.8                                            ONEGM.sup.3                                                                              58.2    -188.2    252.8                                            ______________________________________                                         .sup.1 Nitromalonate polyester according to formula (I) where R.sup.1 is      --NO.sub.2 and R.sup.2 is --H.                                                .sup.2 Nitromalonate polyester according to formula (I) where R.sup.1 and     R.sup.2 are --R.sup.3 ONO.sub.2 and R.sup.3 is --CH.sub.2 --.                 .sup.3 Nitromalonate polyester according to formula (I) where R.sup.1 are     R.sup.2 are --NO.sub.2.                                                  

The data in Table D indicates the clear superiority of the nitromalonatepolyesters of the present invention or conventional binder systems.

What we claim is:
 1. A nitromalonate polyester having the generalformula: ##STR42## where R¹ and R² are the same or different and areselected from --NO₂, --R³ ONO₂, alkyl, --F and --H with the proviso thatat least one of R¹ and R² is --NO₂ or --R³ ONO₂ ;R³ is alkylene; x is##STR43## R⁵ is --CH═CH or --CH₂ CH₂ --; R⁶ is alkylene; n is at eachindependent occurence an integer from 1 to about 40; and x is aninteger.
 2. The nitromalonate polyester of claim 1 wherein R¹ and R² are--CH₂ ONO₂ and X is --H.
 3. The nitromalonate polyester of claim 1wherein both R¹ and R² are --NO₂.
 4. The nitromalonate polyester ofclaim 1 wherein both R¹ and R² are --CH₂ ONO2.
 5. In a solid propellantcomprising a polymeric binder, binder curing agent, oxidizer andplasticizer, the improvement comprising an effective amount of apolymeric binder which has the general formula: ##STR44## where R¹ andR² are the same or different and are selected from --NO₂, --R³ ONO₂,alkyl, --F and --H with the proviso that at least one of R¹ and R² is--NO₂ or --R³ ONO₂ ;R³ is alkylene; X is ##STR45## R⁵ is --CH═CH or--CH₂ CH₂ --R⁶ is alkylene; n is at each independent occurrence areinteger from 1 to about 40; and x is an integer from 1 to about
 40. 6.The solid propellant of claim 5 wherein both R¹ and R² are --NO₂.
 7. Thesolid propellant of claim 5 wherein both R¹ and R² are --CH₂ ONO₂. 8.The solid propellant of claim 5 wherein the plasticizer is substantiallyfree of butanetriol trinitrate.